The field of the present invention is reciprocating air driven devices and specifically the air valves therefor.
Reciprocating air driven devices have long had the advantage that they can be employed in circumstances and environments where motors and engines are inappropriate. One area of concern with engines and motors is their use in an environment with combustibles. Sparks and hot manifolds can potentially cause ignition of such combustibles with engines and motors.
Even with air driven devices, as with any operating mechanism, sparks resulting from static charges cannot be ruled out under all conditions. Some of the smaller versions of such air driven mechanisms are now made of engineering plastics rather than conductive metal. Such plastics are typically not conductive and cannot be grounded. Therefore, a mechanism may be warranted to avoid static charge buildup and provide an ability to ground the device.
One mechanism for avoiding the buildup of static charge is to blend a conductive filler into the structural plastic. Carbon and metal fibers are typically considered as fillers for the transformation of plastics from statically insulative to statically dissipative. However, such fillers have been determined to adversely effect the longevity of sealing members required to slide on the filled plastic such as in air valves for driving and controlling such devices.
One such application of plastic for reciprocating air driven devices is for air operated double diaphragm pumps which include reciprocating air valves for the control and driving of the pumps. Valve elements having annular seals thereabout sliding within valve bodies are typically used in such air valves. Such arrangements can encounter the aforementioned seal longevity problem. The following patents illustrate a long line of pumps, air valves therefor and details in the construction thereof, the disclosures of which are incorporated herein by reference:
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